1902 Encyclopedia > Anchor > Common Anchor. Testing of Anchors. Size of Anchors.
Common Anchor. Testing of Anchors. Size of Anchors.
Fig. 1 -- Common Anchor
Fig. 1 represents the "common" anchor. The various parts are known by the following terms:- The shank is the straight part, ab; the square, ac, is the part of the shank to which the stock and the shackle are attached; d is the crown; de and df the arms; gg the palms or flukes; the pee, the bill, or the point is the extreme end of the arm beyond the palm; the blade is the part of the arm at the back of the palm; h is the shackle or ring to which the cable is attached; kl is the stock, placed at right angles to the plane of the arms and shank. The use of the stock is to "cant" the anchor. If it falls with the arms on the ground, the other end resting on the end of the stock, the pull of the cable will turn it over, so that the stock will lie upon the ground, and the weight of the crown and arms then resting upon the sharp point, will cause it to enter the soil and take fast hold.
The stock is made of iron in anchors of 60 cwt. and under, and of wood for anchors above that weight. a wooden stock (fig. 8)is made of English oak in two pieces; they are scored over the square so as to leave a space of about 2 in. clear betwen them at the shank and to touch at the extremities. It is made of parallel for about 1/6th of its length at the centre, tapering from thence to the extremities, the side next the shackle being kept straight and the remaining three sides tapered. The section at any part is square, the dimensions being 1/10th of the length at the centre and half of this at the ends. The two pieces are fastened together by four iron bolts near the shank, six or eight treenails, and six iron hoops at the ends. Th hoops are driven on tightly while hot, so that the contraction of the iron in cooling may draw the parts closely together. A projection termed a nut, shown by the dotted lines at a, a, in fig. 8, is left on the square to prevent any lateral motion of the stock. An iron stock is made in one forging, so as to pass through a hole a, punched in the square. the stock has a shoulder b, which fits againts the side of the shank when it is in the position for action as in fig. 1, and it is secured by a key driven tightly on the other side of the shank. The advantage of this is, that the stock can be unshipped and laid along the shank for convinience of stowing, as shown in fig. 4. The weight of the stock, whether of wood or iron, is about 1/6th that of the anchor.
Fig. 4 -- Iron stock unshipped for stowing
The shank and each arm are forged under the steamhammer in three pieces, and are then welded together at m and n, fig. 8. The welding is done by the "Hercules," which is a heavy iron ram placed over an anvil, so that it can be raised by a steam power to a height of some 9 or 10 feet, and then let fall, being guided in its descent by three men, who hold rods attached to it. It is needless to say that the welding must be carefully done, as the whole strength of the anchor depends upon it.
Testing of Anchors
To ensure the safety, every anchor should be tested at public testing-house to 1/3rd of its breaking strain. The anchor is held by a chain attached to the shackle, and the strain is applied to each arm separately at one 1/3rd of its length from the point. The proof of the anchor is that it must show no sign of fracture, and that if any deflection is caused by the strain, it must be return very nearly to its original shape. A good anchor, after bing deflected half an inch, will return to its former shape, leaving no permanent set.
Size of Anchors
The size of anchors for various ships has been determined by practice, but is based upon the theory that as the anchor is required to withstand the force brought upon the ship by the wind and the tide, which would otherwise cause her to drift, its strength must be nearly proportional to her resistance. A result which will accord with sound practice may be obtained by calculating the resistance of a given ship at a speed of twelve knots, and taking this for the working load of the anchor. The working load should be half the testing strain, and consequently 1/6th of the breaking strength.
A large iron clad carries 8 anchors -- 2 bower, 2 sheet, 1 stream, 1 stern, and 2 kedge. The bower anchors (fig. 7.) are stowed at the bow, and are for ordinary use in a roadstead; if there is any difference in weight, the heavier is stowed on the starboard side, and is termed the best bower. The sheet anchors (fig. 8) are stowed as far forward as is convenient in the waist of the ship, and are sometimes called the waist anchors; they are only used in cases of emergency, or in the event of any accident befalling the bowers.The stream anchor is for use in a river or sheltered place, where a small anchor is sufficient to hold the ship. The stern anchor is used when there is not room for the ship to swing with the tide. The kedge anchors are generally of different sizes, one large and one small; they are used to warp the ship along a narrow channel, the kedge being carried out in a boat with a hempen cable attached to it, and dropped; the ship can be hauled to the anchor. kedge anhors are still supplied in the Royal Navy, but are very rarely used, the services for which thy are intended being generally performed by the aid of a steam-tug vessel.
Table 1, Table 2 and Table 3 give the sizes and number of anchors and cables carried by ships of the Royal Navy, and those required by Lloyd's rules to be carried in merchant ships. The sheet and bower anchors are of the same size, and are given in the tables under the heading "Bower"
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